1. Field of the Invention
The subject invention is directed to steerable medical devices such as guiding sheaths and handles therefor, which are adapted and configured for the introduction and placement of diagnostic and therapeutic devices into the human vasculature.
2. Description of Related Art
There are many instances where physicians must introduce diagnostic and therapeutic devices such as diagnostic and therapeutic electrodes, ultrasound transducers, biopsy devices and other surgical tools into the body. The diagnostic and therapeutic devices are often carried by catheters which allow physicians to gain access to the body in a minimally invasive manner by way of bodily lumens. In cardiac treatment, for example, a catheter is advanced through a main vein or artery into the region of the heart that is to be treated.
Guiding catheters and sheaths are commonly used to introduce balloon catheters and stents into the vascular system (e.g., for percutaneous transvascular coronary angioplasty), to introduce cardiac pacing leads into the coronary sinus (e.g., for left ventricular pacing and cardiac resynchronization procedures), or to introduce radiofrequency ablation catheters into the left atrium (e.g., for treatment of atrial fibrillation) or into the renal artery for renal denervation procedures.
Guiding catheters and sheaths typically come in French sizes ranging from 4 F all the way to 12 F, in some cases even 18 F. Some examples feature an inner lumen extending from the proximal portion all the way to the distal tip section. The inner lumen often has a PTFE liner to make the insertion of a device therethrough as easy and as smooth as possible.
One method of introducing diagnostic and therapeutic apparatus into the body is to introduce a tubular member (typically a “sheath”) into the vicinity of the targeted region. A diagnostic or therapeutic apparatus is then passed through the tubular member to the targeted region. If necessary, the diagnostic or therapeutic apparatus may be removed after its function is performed, but the tubular member can be left in place, so that other apparatuses may be advanced to the targeted region to complete the diagnostic and/or therapeutic procedure.
Precise placement of the diagnostic or therapeutic apparatus is very important, especially in those procedures concerning the heart. To that end, some conventional sheaths are guided to the targeted region with a steerable catheter that is located within the sheath lumen. Once the sheath reaches the targeted region, the steerable catheter is removed from the sheath and a catheter carrying the diagnostic or therapeutic apparatus is advanced through the lumen. This type of sheath lacks any onboard steering mechanism. As a result, redeployment of the distal portion of sheath, even to a region in close proximity to the initially targeted region, requires the withdrawal of the diagnostic or therapeutic apparatus and the reintroduction of the steering catheter.
Other conventional sheaths include a steering mechanism that allows the physician to deflect the distal portion of the sheath. The steering mechanism consists primarily of one or more steering wires. One end of each steering wire is secured to the distal end of the sheath, while the other end is secured to a steering control device, such as the rotating cam and steering control knob arrangement commonly found in steerable catheters.
A major shortcoming of currently manufactured steerable guiding sheaths is that the steering mechanism and or the deflection of the distal sheath section is not precise enough, and or might require different steering precision and/or maximum steering angle for different applications and intended uses. For example, to deliver a larger ablation catheter into the left atrium to treat atrial fibrillation, it might require a steerable guiding sheath with a 1:1 gear ratio to achieve tip deflection of up to 270 degrees in both directions, while the delivery of an ablation catheter through the sheath into the renal artery might require a very precise deflection control and a gear ratio of 3:1 with a deflection of only 90 degrees in both directions. Also it takes more force to deflect a 14 F guiding sheath or catheter as compared to a 6 F guiding sheath or catheter.
There is therefore a need in the art for improved steerable guiding sheaths, catheters, dilators, and handle assemblies which provide relatively precise directional steering and versatility.